As said above, you have to check either via VASA plugin or from SAN team, in case if the error occurred because of less free space in thin lun, you should see appropriate SCSI sense codes in vmkernel log of the server

Usually you can see in log something like "failed H:0x8 D:0x0 P:0x0 Possible sense data: 0xA 0xB 0xC"

In the above sense code

0xC is the plugin code which will give you information on the thin provisioned lun

following are the relevant code

06h Allocating more thin provision space. Device server is in the process of allocating more space in the backing pool for a thin provisioned LUN.